Traditional doors and windows have three important components, the frame, the shutter and-the fixtures. The frame and shutter are normally made from well seasoned wood and the fixtures are made of iron, anodised metals or aluminum.
Increasing scarcity and high cost of good timber has considerably increased the utility of precast R.C.C. door and window frames, which are not only durable but also markedly economical and easy to produce. Many enterprising people who have been making cement articles and selling them in semi-urban areas have also started manufacturing R.C.C door and window frames.
Materials Used
Cement concrete, M200 grade, with well graded coarse and fine aggregates should be used for making these frames. The maximum nominal size of aggregate should not exceed 10 mm. Mild steel bars are normally, used as reinforcement.
Section of Frames
The cross section of frames is usually 100 mm x 60 mm or 70 mm x 75 mm for single shutter doors. Three bars of 6 mm diameter are provided as minimum reinforcement. The bars should be held firmly by means of 3 mm diameter steel wires spaced at not more than 300 mm centre to centre. A concrete cover of 12 mm
should be provided for the main bars.
Moulds
Properly. seasoned timber of good quality should be used for preparing the moulds. They should be stiffened suitability to prevent loss of shape. Fix-up devices and hold fasts should be incorporated in the mould at the casting stage itself. The moulds for doors qd windows can be for individual members of the frame or for
the whole frame.
Casting and Curing
It is preferable to cast the horizontal and vertical members of the frame separately, as it will avoid difficulties in transport and handling. One of the main reinforcement bars has a suitable projection, or a separate bar may be placed centrally in the vertical member to locate itself into holes provided at the corresponding points in the horizontal member at the top. The horn projections of the horizontal member are optional.
After pouring concrete into the mould.it should be vibrated with mechanical vibrators. The frames nlay be removed from the mould, 24 hours after casting. They should be cured under water for at least 4 days followed by maturing period of 24 days at a covered place before they are ready to be used.
Fixing Devices and Holdfasts
The frames should be held in position with the help of holdfasts which are inserted at the time of casting the frames. The projecting portion of the holdfasts should be firmly embedded in the wall with concrete. Arrangemeilts are to be made in the frame for receiving tower bolts etc. A 6 mm thick M.S plate, long enough to project out of the frame at the appropriate place, is welded to one of the main reinforcement bars. This projected portion has a hole to receive the tower bolt which is fixed to the door leaf.
Erection
The vertical members should be held in position with the help of suitable supports and the horizontal member is placed over them. The joints between the members are grouted with cement-sand slurry (1:2), and neatly pointed flush. The assembled frame should be plumbed correctly before the holdfasts are fixed in the walls with cast-in-situ concrete.
Fixing Shutters
Shutters should be fixed to frames with the help of hardwood blocks which are bolted to the styles (verticals) of the R.C.C frame. Hard wood blocks 150 mm long and 45 or 50 mm x 30 mm cross section, with holes to allow insertion of two 6 mm diameter, M. S. bolts, rnay be used for fixing the shutters.
Suitable spacers should be kept in the mould at the hinge positions, while casting the frames, with the help of 6 mm diameter M. S. bolts, nuts and washers.
Special Considerations
The cast members of the frames should be handled with care to avoid cracking and damage to edges which cannot be repaired satisfactorily. Hammering of any kind should be avoided while fixing the frames and shutters. The quality and surface finish of the frames can be improved by vibration and use of well prepared moulds. The frame may be painted.
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